Many hybrid vehicles, which make use of both an electric motor and an internal combustion engine for propulsion, include a start-stop system which automatically stops the internal combustion engine when there is a low power demand, thereby increasing fuel economy and reducing emissions. The start-stop system then restarts the internal combustion engine when power demand is increased and more power is required.
More particularly, a typical start/stop system employs controls that turn off the internal combustion engine when there is little or no power demand, such as during idle conditions and during vehicle braking and coasting situations. The internal combustion engine will then be commanded to start up again as soon as more power is required.
Start/stop strategies place a much higher durability burden on the traditional electric starter system, requiring a much more robust starter, alternator and battery. Some vehicle configurations include the addition of a belt driven starter generator. Another option is to integrate a starter generator on the flywheel. However, these strategies are at additional cost. Another aspect of employing engine start/stop strategies is the potential for increased engine wear, due to the more frequent starts and the lack of lubrication until the engine oil pump has built up suitable oil pressure.
Ordinarily an electrically driven starter motor is used to start the internal combustion engine. An alternative to using electric power for starting the engine is to use hydraulic power. The use of a hydraulic starter motor to start an engine is known, particularly to start large internal combustion engines (e.g. heavy road construction equipment) instead of an electrically driven starter.